LTC3218
400mA Single Wire
Camera LED Charge Pump
FEATURES
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DESCRIPTION
The LTC
®
3218 is a low-noise, high-current charge pump
DC/DC converter capable of driving high current LEDs at up
to 400mA from a 2.9V to 4.5V input. A low external parts
count (one flying capacitor, two programming resistors and
two bypass capacitors at V
IN
and CPO) make the LTC3218
ideally suited for small, battery-powered applications.
Built-in soft-start circuitry prevents excessive inrush cur-
rent during start-up. High switching frequency enables the
use of small external capacitors. A built-in 2-second timer
protects the LED during flash mode.
Output current level is programmed by an external re-
sistor. LED current is regulated using an internal high
side 220mΩ sense resistor. Automatic mode switching
optimizes efficiency by monitoring the voltage across the
charge pump and switching modes only when dropout
is detected. The part is available in a low profile 3mm
×
2mm 10-lead DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 6411531.
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Low Noise Constant-Frequency Operation
Multi-Mode Operation: 1x or 2x Boost Mode
Automatic Mode Switching
High Output Current: 150mA (Continuous), 400mA
(Pulsed) From Li-Ion/Polymer Input
2-Second Flash Current Timeout for LED Protection
Automatic Soft-Start
Output Disconnect
No Inductors
220mΩ Internal High Side Current Sense Resistor
Single Resistor Programming Capability
Tiny Application Circuit (3mm
×
2mm DFN Package,
All Components < 1mm High)
APPLICATIONS
■
LED Torch/Flash Supply for DSCs/Cellphones
TYPICAL APPLICATION
Efficiency vs V
IN
2.2μF
100
90
CP
2.9V TO 4.5V
2.2μF
V
IN
CM
CPO
LTC3218
I
LED
GND
I
SETT
40
2.9
10.2k
1%
3.1
3.3
3.5
3.7
V
IN
(V)
3218 TA01b
4.7μF
EFFICIENCY (%)
80
70
60
50
50mA
150mA
300mA
3.9
4.1
4.3
4.5
DISABLED
DISABLED
ENABLED
ENABLED
ENF
ENT
I
SETF
LED
AOT2015
ENF
0
0
1
1
ENT
0
1
0
1
I
LED
0 (SHUTDOWN)
100mA (TORCH)
290mA
390mA (FLASH)
3218 TA01
3218fb
1
LTC3218
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
CP 1
CPO 2
I
LED
3
ENT 4
I
SETT
5
11
10 V
IN
9
8
7
6
CM
GND
ENF
I
SETF
V
IN
to GND ................................................... –0.3V to 6V
CPO to GND ................................................ –0.3V to 6V
ENF ENT ........................................... –0.3V to V
IN
+ 0.3V
,
I
CPO
, I
ILED
(Note 2) ...............................................500mA
CPO Short-Circuit Duration .............................. Indefinite
Storage Temperature Range................... –65°C to 125°C
Operating Temperature Range (Note 3).... –40°C to 85°C
DDB PACKAGE
10-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3218EDDB#PBF
TAPE AND REEL
LTC3218EDDB#TRPBF
PART MARKING
LCHS
PACKAGE DESCRIPTION
10-Lead (3mm
×
2mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Power Supply
V
IN
Operating Voltage
I
VIN
Operating Current
I
VIN
Shutdown Current
LED Current
Torch Current Ratio
(I
LED
/I
SET
)
Flash Current Ratio
(I
LED
/I
SET
)
Flash Current Ratio
(I
LED
/I
SET
)
I
LED
Dropout Voltage (V
ILED
)
Mode Switching Delay (LED Warm-Up Time)
Turn-On Time
Minimum LED Forward Voltage
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 3.6V, C
IN
= C
FLY
= 2.2
μ
F C
CPO
= 4.7
μ
F ENF = HIGH, unless
,
,
otherwise noted.
CONDITIONS
●
MIN
2.9
TYP
MAX
4.5
UNITS
V
μA
mA
I
CPO
= 0mA, 1x Mode
I
CPO
= 0mA, 2x Mode
ENF = ENT = LOW, V
CPO
= 0V
I
LED
= 50mA
ENT = HIGH, ENF = LOW
I
LED
= 150mA
ENT = LOW, ENF = HIGH
I
LED
= 150mA
ENT = ENF = HIGH
Mode Switching Threshold,
Δ(V
CPO
– V
ILED
),
I
LED
= 100mA
ENF ENT
,
I
LED
= 50mA
to LED Current On
●
●
980
1.7
1.1
765
2205
2970
850
2450
3300
7
0.5
160
2.2
3
935
2695
3630
μA
A/A
A/A
A/A
mV
ms
μs
V
3218fb
2
LTC3218
ELECTRICAL CHARACTERISTICS
PARAMETER
Charge Pump (CPO)
Charge Pump Output Clamp Voltage
1:1 Mode Output Impedance
1:2 Mode Output Impedance
CLK Frequency
CPO Short Circuit Detection
Threshold Voltage
Test Current
ENF ENT
,
High Level Input Voltage (V
IH
)
Low Level Input Voltage (V
IL
)
Input Current (I
IH
)
Input Current (I
IL
)
Flash Timeout
ISETF, ISETT
V
ISET
I
ISET
I
SET
= 110μA
ENT = LOW, ENF = HIGH
●
●
●
●
The
●
denotes the specifications which apply over the full operating
,
,
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 3.6V, C
IN
= C
FLY
= 2.2
μ
F C
CPO
= 4.7
μ
F ENF = HIGH, unless
otherwise noted.
CONDITIONS
MIN
TYP
5.3
1.3
7
1
ENT = HIGH
ENT = ENF = LOW, V
CPO
= 0V
●
●
MAX
UNITS
V
Ω
Ω
MHz
0.6
20
1.4
1.5
50
V
mA
V
0.4
14.4
–1
2
1.18
1.21
1.24
181
30
1
V
μA
μA
s
V
μA
V
EN
= 3.6V
V
EN
= 0V
ENF = HIGH
●
●
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
Based on long-term current density limitations. Assumes an
operating duty cycle of ≤ 10% under Absolute Maximum Conditions
for durations less than 10 seconds. Maximum current for continuous
operation is 150mA.
Note 3:
The LTC3218E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C ambient
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
TYPICAL PERFORMANCE CHARACTERISTICS
I
LED
Dropout Voltage
vs LED Current
0.009
0.008
DROPOUT VOLTAGE (V)
0.007
0.006
I
LED
(mA)
0.005
0.004
0.003
0.002
0.001
0
0
200
300
100
LED CURRENT (mA)
400
3218 G01
T
A
= 25°C, unless otherwise noted.
I
LED
vs R
SET
450
400
350
300
250
200
150
100
50
0
0
50
100
150 200
R
SET
(kΩ)
250
300
350
V
IN
SHUTDOWN CURRENT (μA)
TORCH
FLASH (ENT = LOW,
ENF = HIGH)
FLASH (ENT = ENF = HIGH)
3.0
2.5
2.0
V
IN
Shutdown Current vs V
IN
T = 25°C
T = –40°C
1.5
T = 85°C
1.0
0.5
0
2.9
3.1
3.3
3.5
3.7
V
IN
(V)
3.9
4.1
4.3
4.5
3218 G02
3218 G03
3218fb
3
LTC3218
TYPICAL PERFORMANCE CHARACTERISTICS
1x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
1.8
OPEN-LOOP OUTPUT RESISTANCE (Ω)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–40
–15
35
10
TEMPERATURE (°C)
60
85
3218 G04
T
A
= 25°C, unless otherwise noted.
2x Mode Charge Pump
Open-Loop Output Resistance
(2V
IN
– V
CPO
)/I
CPO
vs Temperature
10
OPEN-LOOP OUTPUT RESISTANCE (Ω)
9
8
FREQUENCY (kHz)
7
6
5
4
3
2
1
0
–40
–15
35
10
TEMPERATURE (°C)
60
85
3218 G05
Oscillator Frequency vs V
IN
1100
1080
T = –40°C
1060
1040
1020
T = 85°C
1000
980
960
2.9
T = 25°C
I
CPO
= 50mA
V
IN
= 2.9V
V
IN
= 3.6V
V
IN
= 3.6V
V
IN
= 4.5V
3.1
3.3
3.5
3.7
V
IN
(V)
3.9
4.1
4.3
4.5
3218 G06
Torch Mode I
LED
/I
SET
Current Ratio
vs I
LED
Current
1400
1300
1200
CURRENT RATIO
CURRENT RATIO
1100
1000
900
800
700
600
500
400
50 60 70 80 90 100 110 120 130 140 150
I
LED
CURRENT (mA)
3218 G07
Flash I
LED
/I
SET
Current Ratio
vs I
LED
Current
(ENT = LOW, ENF = HIGH)
3500
3300
3100
CURRENT RATIO
2900
2700
2500
2300
2100
1900
1700
1500
100
150
250
300
200
I
LED
CURRENT(mA)
350
400
4500
4300
4100
3900
3700
3500
3300
3100
2900
2700
Flash I
LED
/I
SET
Current Ratio
vs I
LED
Current
(ENT = ENF = HIGH)
2500
100
150
250
300
200
I
LED
CURRENT(mA)
350
400
3218 G08
3218 G09
Torch Mode I
LED
Current vs V
IN
160
140
R
SETT
= 7.49k
120
I
LED
(mA)
I
LED
(mA)
100
80
60
40
20
0
2.9
3.1
3.3
3.5
3.7
V
IN
(V)
3218 G10
Flash Mode I
LED
Current vs V
IN
(ENT = ENF = HIGH)
450
400
350
300
250
200
150
100
50
R
SETF
= 40.2k
R
SETF
= 20k
I
LED
(mA)
R
SETF
= 10.2k
450
400
350
300
250
200
Flash Mode I
LED
Current vs V
IN
(ENT = LOW, ENF = HIGH)
R
SETF
= 7.49k
R
SETF
= 10.2k
R
SETT
= 10.2k
R
SETT
= 20k
R
SETT
= 40.2k
R
SETF
= 20k
150
100
50
R
SETF
= 40.2k
3.9
4.1
4.3
4.5
0
2.9
3.1
3.3
3.5
3.7
V
IN
(V)
3.9
4.1
4.3
4.5
0
2.9
3.1
3.3
3.5
3.7
V
IN
(V)
3.9
4.1
4.3
4.5
3218 G11
3218 G12
3218fb
4
LTC3218
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs V
IN
100
90
EFFICIENCY (%)
80
70
60
50
40
2.9
T
A
= 25°C, unless otherwise noted.
2x Mode CPO Output Ripple
50mV/DIV
AC COUPLED
50mA
100mA
150mA
200mA
300mA
3.1
3.3
3.5
3.7
V
IN
(V)
3218 G13
V
IN
= 3.6V
I
CPO
= 200mA
4.5
500ns/DIV
3218 G14
3.9
4.1
4.3
PIN FUNCTIONS
CP CM (Pin 1, Pin 9):
Charge Pump Flying Capacitor. A
,
2.2μF X5R or X7R ceramic capacitor should be connected
from CP to CM.
CPO (Pin 2):
Output of the Charge Pump. This pin may
be enabled or disabled using the ENT and ENF inputs.
A 4.7μF X5R or X7R ceramic capacitor is required from
CPO to GND.
I
LED
(Pin 3):
LED Current Output. The LED is connected
between I
LED
(anode) and GND (cathode). The current
out of the I
LED
pin is set by resistors connected to the
I
SETT
and I
SETF
pins. An internal, 220mΩ sense resistor
is connected between CPO and I
LED
ENT (Pin 4):
Input. The ENT pin is used to enable the
part into torch mode and bring it into shutdown mode.
An internal 250kΩ resistor pulls this pin to GND when
left floating.
I
SETT
(Pin 5):
LED Torch Current Programming Resistor.
A resistor connected between this pin and GND is used
to set the LED torch current level.
I
SETF
(Pin 6):
LED Flash Current Programming Resistor.
A resistor connected between this pin and GND is used
to set the LED flash current level.
ENF (Pin 7):
Input. The ENF pin is used to enable the
part into flash mode and bring it into shutdown mode.
An internal 250kΩ resistor pulls this pin to GND when
left floating. A safety timer will disable the part if this pin
is held high for more than 2 seconds.
GND (Pin 8):
Ground. This pin should be connected directly
to a low impedance ground plane.
V
IN
(Pin 10):
Power. Supply voltage for the LTC3218. V
IN
should be bypassed with a low impedance ceramic capaci-
tor to GND of at least 1.6μF of capacitance.
Exposed Pad (Pin 11):
Ground. This pad must be soldered
to a low impedance ground plane for optimum thermal
performance.
3218fb
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